The increasing availability of information in the form of data from various sources has spurred large public demand for broadband data transfer that challenges the capabilities of communication delivery systems. The number of information sources publicly and interactively available via the internet to personal computers, as well as private data network sources, continues to proliferate. Full motion video programming and source material also has rapidly progressed from early television broadcasting and cable distribution networks to a wide variety of distribution arrangements, including direct broadcast satellite television. The number of full motion video sources has expanded in response to increased usage and user demand for a greater range of subject matter content.
To meet user requirements, more robust broadband networks have evolved. For example, Litteral et al. U.S. Pat. No. 5,247,347 discloses a digital video distribution network providing subscribers with access to multiple Video On Demand service providers through the public switched telephone network. The subscriber may transmit ordering information via the public switched telephone network to the independent video information providers. Video programming may be accessed and transmitted to the subscriber directly from a video information provider (VIP) or through a video buffer located at a central office (CO) serving the subscriber. Connectivity between the central office and the subscriber for transmission of video data is provided by an asymmetrical digital subscriber line (ADSL) system. ADSL, which has been standardized by ANSI as T1.413, uses existing unshielded twisted pair copper wires from the telephone company central office to the subscriber's premises. Equipment at the central office and the subscriber's premises permits transfer of more high speed digital information signals to the subscriber than in the reverse direction. In the Litteral et al. patent, ADSL interface units at the central office multiplex digital video information with voice information to be transmitted to the subscriber and support two-way transmission between the subscriber's line and the X.25 packet data network of one or more control channels. A complementary ADSL interface unit at the subscriber's premises separates downstream video control signals and voice telephone signals from the line and multiplexes upstream control signals and voice telephone signals onto the line. A similar public switched telephone network multimedia information ADSL delivery system is disclosed, for example, in U.S. Pat. No. 5,528,281 to Grady et al.
A number of patents have proposed various schemes for wireless distribution of information. Hylton et al. U.S. Pat. No. 5,613,191, for example, describes provision of interactive multimedia services including broad band video and audio data and control signals in a multiplexed form to subscriber premises via a communications link from a plurality of information providers. Real time encoders receive video programs and encode the information for those programs into packets of compressed digital data, e.g., in accord with a recognized video compression standard. The head end may also receive previously encoded video program material from other sources, such as a digital server or a digital transmission media. Multiplexers combine digital data for groups of programs into the multiplexed packet data streams. A digital modulator, such as a 64 or 256 QAM modulator, modulates each digitally multiplexed packet data stream for transport in one unique channel. A combined spectrum signal containing these channels is delivered to the subscribers' premises through suitable multimedia distribution and delivery architecture. The combined spectrum signal channel is connected to a network interface at the subscriber premises where it is up-converted to place the channels into available frequency channels in the UHF range. The unique channel from each digital modulator is fed to an up-converter synthesizer module which performs a frequency hopping spread spectrum technique. At the receiver site within the premise an antenna receives a signal which is then down-converted and supplied to a wireless signal processor. The wireless signal processor, typically part of an interface module connected by a cable to the down-converter, processes the received wireless signal to select one of the channels.
While developments such as the systems described above have advanced communication capabilities, limitations remain with respect to meeting the increasing requirements relating to volume of transmission, efficiency and flexibility. Network based systems that deliver data over twisted pair copper wire, even under ADSL communication conditions, are bandwidth limited.
The network data packet transmission modes, such as ATM and the like that have been developed to transport large quantities of video data with high speed and flexibility, contain significant cell overhead that dilutes the proportion of data information payload. ATM networks communicate all information in cells that comprise a well defined and size-limited header area and a user information, or payload, area. CCITT.121/2, the standardized ATM cell format, specifies a 5-byte header field and a 48-byte information or payload field. The header field carries information pertaining to ATM functionality, such as identification of the cells needed for routing purposes. Transfer is asynchronous in the sense that the recurrence of cells that contain information from any particular sender is not necessarily periodic. Each sending device using the ATM network submits a cell for transfer when it has a cell to send, not in accordance with a transmission time slot assigned to the device. The cell overhead is required to enable the ATM switch, or a plurality of ATM switches throughout the network, to rout the transport of cells within the switch and to translate the header information in the cells for appropriate routing of the succeeding ATM cell receiving element.
Wireless communication is less restrictive than the twisted pair wire plant insofar as bandwidth is concerned and does not require the cell overhead of network data transmission arrangements. Thus, cells received over the data network can be stripped of substantial cell overhead for wireless transmission over the subscriber final link. With wireless transmission, however, the signal strength of the radio link is subject to variation with physical conditions and distance. The quality of service of such data transmission thus can be degraded to an unacceptable bit error rate, particularly with transmission at high data rates. Without cognizance of the signal strength and bit error rate over each subscriber radio link, quality of service cannot be accurately assured.
The above-referenced commonly assigned copending application (Attorney Docket 680-224) addresses the shortcomings of prior systems by providing a wireless, cellular radio link for broadband data distribution from a base station to a plurality of subscriber stations within the cell reception area. Buffers in the base station, associated with respective subscribers, collect the requested data from the information providers for transmission by the base station in a statistical time division multiplexed (STDM) fashion, whereby each subscriber may be assigned a minimum transmission time interval during which data will be transferred from the associated buffer.
In order for such an arrangement to service multiple individual recipients of wireless signals from a given transmission source who may require different levels of transmission quality and different data throughput rates, collectively referred to herein as quality of service levels, an efficient and flexible STDM multiplexer is essential. For example, subscribers who are to receive real time video data would require a greater throughput rate and lower bit error rate than subscribers to whom text is to be downloaded for storage. Other users may require each of these modes at different times but have no avail for subscribing to different quality of service levels on a scheduled or dynamic basis. The ability to transmit at high bit rates with low bit error rates is dependent upon transient physical conditions. An STDM controller should be able to accommodate, to the greatest extent possible, existing factors such as current user activity, current requirements of various users, and transmission quality conditions.
For example, if the transmission quality becomes degraded in the link to a user who needs high throughput with a low bit error rate, adjustment must be made if the required levels are to be maintained. Such adjustment may involve transmission at a lower bit rate for a longer transmission time interval. The throughput can thus remain the same while the lower transmission bit rate should provide a better bit error rate. The longer transmission time interval for that user can be obtained if a correspondingly shorter transmission time interval can be distributed among other system users. This objective can be realized if there are less than the maximum number of users active. At less than full system capacity, transmission time that would have been allocated to the non-active users is free for use by others. Another adjustment possibility would be to allocate shorter transmission time intervals to users having less stringent transmission throughput requirements to balance the increased transmission time required by the high throughput user, while remaining within the limits of system transmission capacity. Shorter transmission times for other users can also be accomplished by increasing the transmission bit rates for those users, if their transmission link quality is high or their bit error rate requirements are relatively low. The STDM thus should be capable of adjusting, on a dynamic basis, the bit rates and transmission time intervals of all users at any given time if it is to meet all users' requirements, including those video users with the more stringent requirements.